1. Field of the Invention
This invention relates to a low-NOx burner.
2. Description of the Related Art
Generally, reduction of NOx produced during combustion is an essential challenge for gas burners used for a boiler, a cold/hot water producer or the like.
For reduction of NOx, there are various techniques: 1) a thick and thin fuel combustion, 2) multi-stage combustion of fuels or oxidizers, 3) premix lean combustion, 4) exhaust gas recirculation (EGR), 5) steam or water injection, and so on. Most of conventional low-NOx burners include a mechanism for employing these techniques singly or in combination in order to reduce NOx emission.
At present, the strictest regulation against NOx emission concentrations is instituted on combustion appliances used for a boiler, cold/hot water producer and so on. For example, the approval low-NOx standard mandated by Tokyo municipality is the NOx emission concentration of 60 ppm (a converted value in O2=0%, (the same hereinafter)) or less.
Consequently, recent low-NOx burners are designed to reduce NOx emission to a target of 60 ppm or less which is the approval low-NOx standard mandated by Tokyo municipality, most of which carry out combustion at a NOx emission concentration of the order of 40 ppm to 60 ppm.
Instead of implementing a reduction in NOx by the structural design of the burner, some conventional boilers use a water tube serving as a secondary side to cool flame so as to limit the NOx emission concentration to 35 ppm.
However, such technique of cooling flames to reduce NOx needs a structure for cooling the flames, such as the water tube on the secondary side, or the like. For this reason, it is impossible to use this technique for a process heater except for a boiler or a cold/hot water producer.
Until now, it was impossible to limit the NOx emission concentration to 35 ppm or less only by the structural design of the burners. Previously, there has been anticipation for the development of a low-NOx burner which is capable of achieving further reduction of NOx and widely used for things besides the boiler and the cold/hot water producer.
The present invention has been made for responding to the previously discussed conventional needs of the low-NOx burner.
It is therefore an object of the present invention to provide a low-NOx burner further reducing NOx, in comparison with conventional burners, by structural design only.
To accomplish the above object, a low-NOx burner according to a first invention is characterized by including: a nozzle member for injecting a premixture formed by mixing fuel and an oxidizer; and a flame holding member for injecting a premixture or an oxidizer toward the premixture injected from the nozzle member in a direction to intersect the injection direction from the nozzle member.
The low-NOx burner according to the first invention injects the premixture, formed by mixing an oxidizer such as air and fuel and fed into the low-NOx burner, from the nozzle member at high velocity, to induce combustion gas in a furnace to produce self-induced exhaust gas recirculation.
The premixture or oxidizer injected from the flame holding member is blown on the premixture injected from the nozzle member, in the direction in which both injection directions intersect each other, at the downstream position in the injection direction from the nozzle member.
This produces a circulation flow around the meeting point of the premixture injected from the nozzle member and the premixture or oxidizer injected from the flame holding member. The circulation flow serves as an ignition source to hold the flame, resulting in holding the continuous combustion of the burner.
According to the foregoing first invention, since the combustion is produced after the premixture injected from the nozzle member involves and mixes with the exhaust gas in the furnace, it is possible that reduction in oxygen concentration effected by mixing with the exhaust gas reduces a NOx emission concentration. Moreover, since the flame hold is moderately executed, similar to the so-called lifted flame, at a distance from the furnace wall, the flame temperature decreases. This permits further reduction in NOx emission concentration.
To accomplish the above object, the low-NOx burner according to a second invention is characterized, in addition to the configuration of the first invention, in that the injection direction of the premixture from the nozzle member and the injection direction of the premixture or the oxidizer from the flame holding member intersect each other at approximate right angles.
According to the low-NOx burner of the second invention, the premixture or oxidizer injected from the flame holding member is blown on the premixture injected from the nozzle member at an approximate right angle. This improves the flame hold to thereby produce the effect of maintaining a large stable combustion range.
To accomplish the above object, the low-NOx burner according to a third invention is characterized, in addition to the configuration of the first invention: in that a plurality of the nozzle members are circularly arranged on a front face of a body casing of the burner; and in that the flame holding member is situated at the center of the nozzle members which are circularly arranged on the front face of the body casing, and it includes injector orifices which are positioned downstream from the position of the nozzle member in the injection direction and have an axis extending in a direction substantially perpendicular to the injection direction of the nozzle member.
According to the low-NOx burner of the third invention, the premixtures respectively injected from the injector orifices of the flame holding member which is arranged in the front central portion of the body casing, are blown at approximate right angles on the corresponding premixtures injected from a plurality of the nozzle members circularly arranged on the front face of the body casing. On the periphery of the meeting points of both premixtures, circulation flows take place. The circulation flow serves as an ignition source to hold the flame, resulting in holding the continuous combustion of the burner.
To accomplish the above object, the low-NOx burner according to a fourth invention is characterized, in addition to the configuration of the first invention: in that a plurality of the nozzle members are linearly arranged on a front face of a body casing of the burner; and in that the flame holding member is situated at a position opposing to the nozzle members on the front face of the body casing, and it includes injector orifices which are positioned downstream from the position of the nozzle member in the injection direction and have an axis extending in a direction substantially perpendicular to the injection direction of each nozzle member.
According to the low-NOx burner of the fourth invention, the premixtures respectively injected from the injector orifices of the flame holding member which is located at a position opposing the nozzle members, are blown on at an approximate right angle on the corresponding premixtures injected from a plurality of the nozzle members linearly arranged on the front face of the body casing. On the peripheries of the meeting points of both premixtures, circulation flows take place. The circulation flow serves as an ignition source to hold the flame, resulting in holding the continuous combustion of the burner.
To accomplish the above object, the low-NOx burner according to a fifth invention is characterized, in addition to the configuration of the first invention: in that a plurality of the nozzle members are circularly arranged on a front face of a body casing of the burner; and in that a plurality of the flame holding members are concentrically aligned with the nozzle members, and respectively comprise injector orifices which are positioned downstream from the position of the nozzle member in the injection direction and have an axis extending in a direction substantially perpendicular to the injection direction of the nozzle member.
According to the low-NOx burner of the fifth invention, the premixtures injected from the injector orifices of the respective flame holding members which are concentrically aligned with the nozzle members, are blown at an approximate right angle on the corresponding premixtures injected from a plurality of the nozzle members circularly arranged on the front face of the body casing. On the peripheries of the meeting points of both premixtures, circulation flows take place. The circulation flow serves as an ignition source to hold the flame, resulting in holding the continuous combustion of the burner.
To accomplish the above object, the low-NOx burner according to a sixth invention is characterized, in addition to the configuration of the first invention: in that a plurality of the nozzle members and a plurality of the flame holding members are alternated on the same circumference; and in that each flame holding member comprises injector orifices which are positioned downstream from the position of the nozzle member in the injection direction and have an axis extending in a direction substantially perpendicular to the injection direction of the nozzle member.
According to the low-NOx burner of the sixth invention, the premixtures injected from the injector orifices of a plurality of the flame holding members which are alternated with the nozzle members on the same circumference, are blown at an approximate right angle on the corresponding premixtures injected from a plurality of the nozzle members circularly arranged on the front face of the body casing. On the peripheries of the meeting points of both premixtures, circulation flows take place. The circulation flow serves as an ignition source to hold the flame, resulting in holding the continuous combustion of the burner.
To accomplish the above object, the low-NOx burner according to a seventh invention is characterized, in addition to the configuration of the first invention, in that the nozzle member and the flame holding member are respectively communicated with chambers formed independently of each other.
According to the low-NOx burner of the seventh invention, it may be possible to feed premixtures containing different percentages of oxidizer individually into the premixture chamber for supplying the premixture into the nozzle members, and the chamber for supplying the premixture or an oxidizer such as air into the flame holding member, in order to inject the premixtures, different in oxidizer percentage, from the nozzle members and the flame holding member, or to inject only the oxidizer from the flame holding member.
Further, according to the low-NOx burner, it is also possible to independently control flow velocities of the premixture injected from the nozzle member and the premixture or oxidizer injected from the flame holding member.
To accomplish the above object, a combustion method of a low-NOx burner according to an eighth invention is characterized, by including the steps of: injecting a premixture formed by mixing fuel and an oxidizer; and making a premixture impinge on the other premixture in a direction to intersect the injection direction of the other premixture for combustion.
According to the combustion method of the low-NOx burner of the eighth invention, the premixture of the fuel and the oxidizer such as air is injected from the nozzle at high velocity to induce the exhaust gas in the furnace, resulting in creating the self-induced exhaust gas recirculation.
Then, on the downstream side of the injection direction of the above premixture, a premixture injected from another nozzle is blown on the other premixture injected at high velocity such that both injection directions intersect.
This produces a circulation flow on the periphery of the meeting point of the premixture injected and the premixture impinging on the other premixture. The circulation flow serves as an ignition source to hold the flame, resulting in holding the continuous combustion of the burner.
Thus, according to the foregoing eighth invention, since the combustion is produced after the premixture injected into the furnace involves and mixes with the exhaust gas in the furnace, it is possible that reduction in oxygen concentration effected by mixing with the exhaust gas reduces a NOx emission concentration. Moreover, since the flame hold is moderately executed, similar to the so-called lifted flame, at a distance from the furnace wall, a flame temperature decreases. This permits further reduction in NOx emission concentration.
To accomplish the above object, the combustion method of the low-NOx burner according to a ninth invention is characterized, in addition to the configuration of the eighth invention, in that the premixture is blown on the other premixture at an approximate right angle.
According to the combustion method of the low-NOx burner of the ninth invention, the premixture injected from another nozzle is blown at an approximate right angle on the premixture injected into the furnace. This facilitates producing circulation flows which effect the flame hold and thus decreases a flame temperature, resulting in a further reduction of the NOx emission concentration.
To accomplish the above object, a combustion method of a low-NOx burner according to a tenth invention is characterized, by including the steps of: injecting a premixture formed by mixing fuel and an oxidizer; and making an oxidizer impinge on the premixture in a direction to intersect the injection direction of the premixture for combustion.
According to the combustion method of the low-NOx burner of the tenth invention, the premixture of the fuel and the oxidizer such as air is injected from the nozzle at high velocity to induce the exhaust gas in the furnace, resulting in creating the self-induced exhaust gas recirculation.
Then, on the downstream side of the injection direction of the premixture, the oxidizer injected from another nozzle is blown on the premixture such that both injection directions intersect each other.
This produces a circulation flow on the periphery of the meeting point of the premixture injected and the oxidizer impinging on the premixture. The circulation flow serves as an ignition source to hold the flame, resulting in holding the continuous combustion of the burner.
Thus, according to the foregoing tenth invention, the combustion is produced after the premixture injected into the furnace involves and mixes with the exhaust gas in the furnace. This allows reduction in oxygen concentration effected by mixing with the exhaust gas to reduce a NOx emission concentration. Moreover, since the flame hold is moderately executed, similar to the so-called lifted flame, at a distance from the furnace wall, a flame temperature decreases. This permits further reduction in NOx emission concentration.
To accomplish the above object, the combustion method of the low-NOx burner according to an eleventh invention is characterized, in addition to the configuration of the tenth invention, in that the oxidizer is blown on the premixture at an approximate right angle.
According to the combustion method of the low-NOx burner of the eleventh invention, the oxidizer from another nozzle is blown at an approximate right angle on the premixture injected into the furnace. This facilitates producing circulation flows which effect the flame hold, and thus decrease a flame temperature, resulting in a further reduction of the NOx emission concentration.
These and other objects and advantages of the present invention will become obvious to those skilled in the art upon review of the following description, the accompanying drawings and appended claims.